This invention relates to gasification burners in general and more particularly to a gasification burner with improved efficiency and increased safety features.
A gasification burner comprising an antechamber for mixing an at least partly evaporated liquid fuel with primary air; a catalytic device following the antechamber for converting the fuel vapor air mixture into a fuel gas; a mixing chamber adjoining the catalytic device for mixing the fuel gas with secondary air; an annular space which concentrically surrounds the antechamber, the catalytic device and the mixing chamber and is separated from the antechamber by a ring wall; a conically flared combustion chamber and a perforated burner plate of porous material which terminates the combustion chamber and to which the fuel gas-air mixture can be fed from the mixing chamber; a front chamber located ahead of the antechamber, which changes into a ring canal which surrounds the antechamber completely and surrounds the annular space and the catalytic device at least over part of their length; a heat source contained in the ring canal for evaporating the fuel and a heat source contained in the annular space for preheating the primary air during the starting process and for aiding in the event of load changes; radial canals which are contained in the ring wall and which connect the annular space to the antechamber; homogenizing devices, arranged in the antechamber and in the mixing chamber; and an ignition chamber which is arranged between the combustion chamber and the mixing chamber and is separated from the mixing chamber to prevent backfiring is described in U.S. Pat. No. 4,230,443.
In this gasification burner, liquid fuel is burned in two stages. In the first stage only part of the total amount of air supplied is mixed as gasification air (primary air) with the fuel and is converted by partial catalytic oxidation (understoichiometric combustion) into a fuel gas. In the second stage, the fuel gas is mixed with the rest of the air (combustion air, secondary air) and burned at a burner plate.
In domestic burners of conventional design, the fuel is atomized in a nozzle and burned with the total air in a combustion chamber. Since the atomizer output can be varied only within narrow limits, such domestic burners cannot be continuously controlled down to small outputs. Rather, they are planned for maximum output and, if the heating demand is low, are controlled in intermittent operation by means of an on-off control. This necessitates larger boilers as energy accumulators for the pauses in the operation, and further, the repeated starting-up of the burner causes a heavy temperature cycle stress of the materials, an increased soot and pollutant burden for the boiler, flue and exhaust gases as well as excessive power demand during the electric ignition. The gasification burner proposed in the previous patent, on the other hand, needs to be started only at the beginning of a heating period and can then be controlled continuously, according to the heat demand, down to very small outputs, which avoids the disadvantages mentioned. In addition, a substantial reduction of the emission of pollutants such as unburned hydrocarbons and nitrogen oxides in the course of the reaction during the combustion is achieved. The total amount of air required can then be limited to the air required for stoichiometric combustion, whereby high combustion temperatures can be achieved.
One preferred embodiment of the gasification burner proposed in the patent mentioned above is shown in FIG. 1 and consists, as already mentioned, of two stages, i.e., a gasification stage with a centrally arranged reaction chamber 2 (catalytic device) which contains a catalyst, and a combustion part which comprises a mixing chamber 3, an ignition chamber 7 and a conically flared combustion chamber 8 with a terminating porous, perforated burner plate 9. The catalytic device 2 is preceded at its inlet 14 by an antechamber 1 for mixing the fuel with primary air. The antechamber 1 is laterally confined by a ring wall 5 and connected, via radial canals 6 in this ring wall, to an annular space 4, which concentrically surrounds the antechamber 1, the catalytic device 2 and the mixing chamber 3. Through the annular space 4, the primary air is fed to the antechamber 1.
For feeding the fuel in, the antechamber 1 is preceded by a front chamber 10, which becomes a ring canal 11 which surrounds the antechamber 1 completely and the annular space 4 as well as the catalytic device 2 at least over part of their length. The fuel is evaporated at least partly at a first heat source 12 arranged in the ring canal 11 and is mixed in the antechamber 1 with the primary air, which is pre-heated at a second heat source B arranged in the annular space 4, at a first homogenizing device 13, for instance, a swirl vane. The fuel gas generated in the catalytic device 2 is conducted into the mixing chamber 3 and is mixed there at a second homogenizing device 24, for instance, another swirl vane, with secondary air which is fed in.
In an advantageous further embodiment of such a gasification burner, it is further proposed in the previous patent that the reactor chamber 2 (catalytic device) comprises a catalytically inactive container A, at the end faces of which inlet holes 14 and outlet holes 15 are arranged. Furthermore, a perforated disc 16 can be arranged between the mixing chamber 3 and the ignition chamber 7 for protection against backfiring. The ignition chamber 7 can, in addition, be separated from the combustion chamber 8 by a perforated wall 17. For feeding the fuel to the ring canal 11 (evaporation chamber), a fuel connecting nipple 19 is provided; for feeding the secondary air to the mixing chamber 3, a secondary air connecting nipple 23 is provided; and for feeding the primary air to the annular space 4 (preheater chamber), a primary-air feed nipple 26 is provided. At the wall of the ignition chamber 7, a further nipple 27 for an ignition device is also fastened. In the mixing chamber 3 a catalytically inactive lining C, for instance, for ceramic can advantageously be provided.
The housing of the proposed gasification burner is advantageously composed of several parts, for instance, of a cylindrical first housing part 18 surrounding the first stage, with a front cover 20; a middle part 21 surrounding the mixing chamber 3; and a cylindrical end part 25 which carries a conical enlargement surrounding the combustion chamber 8. These housing parts are advantageously made of metal, for instance, stainless steel. In particular, the wall 22 between the mixing chamber 3 and the annular space 4 is made heat conducting, so as to achieve preheating of the primary air in the combustion part.
It has now been found that the proposed gasification burner is prone in some cases to operating trouble. Thus, if the fuel supply fails temporarily, no combustion takes place in the combustion part for a short time. The primay air being fed in is then not pre-heated sufficiently, so that cold air flows through the catalytic part and the latter cools off. When the fuel supply is resumed, the catalytic device then does not work satisfactorily, so that the fuel is only converted incompletely into fuel gas and trouble comes about in the burner, especially soot formation in the combustion part. While it is the express advantage of this burner that very high combustion temperatures can be achieved through stoichiometric air supply, these high temperatures bring with them the danger that the materials used can be destroyed. Thus, the burner plate 9 or the perforated wall 17, for instance, can crack and even the metal housing can become unwelded. To avoid this danger, in the burner proposed in the previous patent application, the end of the device, at which the burner plate is located is fastened to the wall of the boiler, so that the housing is arranged outside the boiler and is cooled by the ambient air. This, however, makes the burner no longer contact-proof, since the danger of injury is considerable if the burner housing is touched. Also, the heat losses which then occur at the housing mean a decrease of the efficiency of the burner.